614 research outputs found
Structures and functions of carotenoids bound to reaction centers from purple photosynthetic bacteria
The photoprotective function of 15,15'-cis-carotenoids bound to the photosynthetic reaction centers (RCs) of purple bacteria has been studied using carotenoids reconstituted into carotenoidless RCs from Rhodobacter sphaeroides strain R26.1. The triplet-energy level of the carotenoid has been proposed to affect the quenching of the triplet state of special-pair bacteriochlorophyll (P). This was investigated using microsecond flash photolysis to detect the carotenoid triplets as a function of the number of conjugated double bonds, n. The carotenoid triplet signals were extracted by using singular-value decomposition (SVD) of the huge matrices data, and were confirmed for those having n = 8 to 11. This interpretation assumes that the reconstituted carotenoids occupy the same binding site in the RC. We have been able to confirm this assumption using X-ray crystallography to determine the structures of carotenoidless, wild-type carotenoid-containing, and 3,4-dihydro-spheroidene-reconstituted RCs. The X-ray study also emphasized the importance of the methoxy group of the carotenoids for binding to the RCs. Electroabsorption (Stark) spectroscopy was used to investigate the effect of the carotenoid on the electrostatic field around P. This electrostatic field changed by 10 % in the presence of the carotenoid
Charged stripes from alternating static magnetic field
We motivate and perform a calculation of the energy of a cold fluid of
charged fermions in the presence of a striped magnetic background. We find that
a non-trivial value for the doping density on the walls is preferredComment: RevTeX, 3 pages, 3 encapsulated PostScript figure
Deconfinement at finite chemical potential
In a confining, renormalisable, Dyson-Schwinger equation model of two-flavour
QCD we explore the chemical-potential dependence of the dressed-quark
propagator, which provides a means of determining the behaviour of the chiral
and deconfinement order parameters, and low-energy pion observables. We find
coincident, first order deconfinement and chiral symmetry restoration
transitions at \mu_c = 375 MeV. f_\pi is insensitive to \mu until \mu \approx
\mu_0 = 0.7 mu_c when it begins to increase rapidly. m_\pi is weakly dependent
on \mu, decreasing slowly with \mu and reaching a minimum 6% less than its
\mu=0 value at \mu=\mu_0. In a two-flavour free-quark gas at \mu=\mu_c the
baryon number density would be approximately 3 \rho_0, where \rho_0=0.16
fm^{-3}; while in such a gas at \mu_0 the density is \rho_0.Comment: 11 pages, 3 figures, epsfig.sty, elsart.st
Dependence of the Chiral Symmetry Restoration Transition on the Quark Self-Energy Kernel
The dependence of the dressed quark propagator on the quark chemical
potential is investigated in various models based on the Dyson-Schwinger
equations. We find that the critical chemical potential of the chiral symmetry
restoration transition is strongly dependent on the nature of the interaction
kernel in the infrared region.Comment: 10 pages, 3 figures, minor change to introduction, accepted for
publication in Phys. Lett.
Shapes of the Proton
A model proton wave function, constructed using Poincare invariance, and
constrained by recent electromagnetic form factor data, is used to study the
shape of the proton. Spin-dependent quark densities are defined as matrix
elements of density operators in proton states of definite spin-polarization,
and shown to have an infinite variety of non-spherical shapes. For high
momentum quarks with spin parallel to that of the proton, the shape resembles
that of a peanut, but for quarks with anti-parallel spin the shape is that of a
bagel.Comment: 8 pages, 5 figures, to be submitted to Phys. Rev. C This corrects a
few typos and explains some further connections with experiment
Stories of success: Cultural narratives and personal stories of elite and professional athletes
Using a narrative methodology to explore the stories Olympic and elite athletes tell about success, we identified three alternatives to the dominant conception of success as the achievement of performance outcomes. In these alternatives, success is storied as: (1) âI did the best that I couldâ â a controllable and sustainable story of effort and application; (2) âItâs the closest thing you can get to flyingâ â a story where success relates to embodied experience and discovery; (3) âPeople I made the journey withâ â which prioritises relationships and connection between people. We reflect on three key insights: (1) success is a multidimensional concept, broader than the singular conception encapsulated within the dominant performance narrative; (2) through various narrative strategies, experienced athletes resist cultural pressures towards a singular conception of success; (3) for long-term performance and well-being, it is necessary to work towards multiple forms of success over time and across contexts
Measures of bioavailable serum testosterone and estradiol and their relationships with muscle strength, bone density, and body composition in elderly men
In the present cross-sectional study of 403 independently living elderly
men, we tested the hypothesis that the decreases in bone mass, body
composition, and muscle strength with age are related to the fall in
circulating endogenous testosterone (T) and estrogen concentrations. We
compared various measures of the level of bioactive androgen and estrogen
to which tissues are exposed. After exclusion of subjects with severe
mobility problems and signs of dementia, 403 healthy men (age, 73-94 yr)
were randomly selected from a population-based sample. Total T (TT), free
T (FT), estrone (E1), estradiol (E2), and sex hormone-binding globulin
(SHBG) were determined by RIA. Levels of non-SHBG-bound T (non-SHBG-T), FT
(calc-FT), the TT/SHBG ratio, non-SHBG-bound E2, and free E2 were
calculated. Physical characteristics of aging included muscle strength
measured using dynamometry, total body bone mineral density (BMD), hip
BMD, and body composition, including lean mass and fat mass, measured by
dual-energy x-ray absorptiometry. In this population of healthy elderly
men, calc-FT, non-SHBG-T, E1, and E2 (total, free, and non-SHBG bound)
decreased significantly with age. T (total and non-SHBG-T) was positively
related with muscle strength and total body BMD (for non-SHBG-T,
respectively, beta = 1.93 +/- 0.52, P < 0.001 and beta = 0.011 +/- 0.002,
P < 0.001). An inverse association existed between T and fat mass (beta =
-0.53 +/- 0.15, P < 0.001). Non-SHBG-T and calc-FT were more strongly
related to muscle strength, BMD, and fat mass than TT and were also
significantly related to hip BMD. E1 and E2 were both positively,
independently associated with BMD (for E2, beta = 0.21 +/- 0.08, P <
0.01). Non-SHBG-bound E2 was slightly strongly related to BMD than total
E2. The positive relation between T and BMD was independent of E2. E1 and
E2 were not related with muscle strength or body composition. In summary,
bioavailable T, E1, total E2, and bioavailable E2 all decrease with age in
healthy old men. In this cross-sectional study in healthy elderly men,
non-SHBG-bound T seems to be the best parameter for serum levels of
bioactive T, which seems to play a direct role in the various
physiological changes that occur during aging. A positive relation with
muscle strength and BMD and a negative relation with fat mass was found.
In addition, both serum E1 and E2 seem to play a role in the age-related
bone loss in elderly men, although the cross-sectional nature of the study
precludes a definitive conclusion. Non-SHBG-bound E2 seems to be the best
parameter of serum bioactive E2 in describing its positive relation with
BMD
FIRI - a Far-Infrared Interferometer
Half of the energy ever emitted by stars and accreting objects comes to us in
the FIR waveband and has yet to be properly explored. We propose a powerful
Far-InfraRed Interferometer mission, FIRI, to carry out high-resolution imaging
spectroscopy in the FIR. This key observational capability is essential to
reveal how gas and dust evolve into stars and planets, how the first luminous
objects in the Universe ignited, how galaxies formed, and when super-massive
black holes grew. FIRI will disentangle the cosmic histories of star formation
and accretion onto black holes and will trace the assembly and evolution of
quiescent galaxies like our Milky Way. Perhaps most importantly, FIRI will
observe all stages of planetary system formation and recognise Earth-like
planets that may harbour life, via its ability to image the dust structures in
planetary systems. It will thus address directly questions fundamental to our
understanding of how the Universe has developed and evolved - the very
questions posed by ESA's Cosmic Vision.Comment: Proposal developed by a large team of astronomers from Europe, USA
and Canada and submitted to the European Space Agency as part of "Cosmic
Vision 2015-2025
Radiogenic isotopes: New tools help reconstruct paleocean circulation and erosional input
Ocean and atmosphere circulation and continental weathering regimes have undergone great changes over thousands of years as well as tens of millions of years. During the glacial stages of the Pleistocene, ocean circulation was generally more sluggish and deep water circulation in the Atlantic had a shallower flow. At the same time, weathering on the continents was enhanced by glacial erosion, particularly in high northern latitudes, which increased the input of erosional detritus into the ocean. In addition, atmospheric pressure gradients were larger, leading to higher wind speeds and increased supply of aeolian dust to the ocean. Prior to the onset of Northern Hemisphere glaciation and pronounced glacial/interglacial cyclicity at âŒ3 m.ya., global climate was warmer than at present. There is also evidence for a more vigorous thermohaline circulation during the early Pliocene
Luteinizing hormone and different genetic variants, as indicators of frailty in healthy elderly men
We investigated the possible clinical correlates between the serum LH
concentration and characteristics of frailty and determined the presence
and concentration of a genetic LH variant in an independently living
population of elderly men. After exclusion of subjects with severe
mobility problems and signs of dementia, 403 healthy men (aged 73-94 yr)
were randomly selected from a population-based sample. Total testosterone
(T), sex hormone-binding globulin (SHBG), and leptin were determined by
RIA. Non-SHBG-bound T was calculated. LH and the presence of the genetic
LH variant were measured using immunofluorometric assays. The
characteristics of frailty were leg extensor strength using dynamometry,
bone mineral density of total body and proximal femur, and body
composition, including lean mass and fat mass, measured by dual energy
x-ray absorptiometry. Disability was further assessed by the Modified
Health Assessment Questionnaire and by a measure of physical performance.
LH significantly increased with age and inversely correlated with T and
non-SHBG-bound T. LH was inversely related to muscle strength and lean
mass, and both relations were independent of T. LH was positively related
to self-reported disability (Modified Health Assessment Questionnaire);
12.5% of the study population was heterozygous for the LH variant allele.
T levels and the degree of frailty were not different in the wild-type LH
group compared with the heterozygote LH variant group. A significant
positive relation between LH and fat mass as well as leptin was only
present in the heterozygote LH variant group. In conclusion, serum LH
levels increases with age in independently living elderly men and
correlates inversely with a variety of indicators of frailty. The observed
relation between LH and frailty, independent of T, suggests that LH
reflects serum androgen activity in a different way than T, possibly
reflecting more closely the combined feedback effect of estrogen and
androgen. A difference in biological response between the two LH forms is
suggested, as a difference exists in the relation between LH and fat mass,
respectively, and leptin in the heterozygote LH variant subjects vs. the
wild-type LH subjects
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